Magnetron apparatus



Jan. 3/1939. R. A. BRADEN MAGNETRON APPARATUS Filed July 22, 1936 2 Sheets-Sheet l 3nventor (Ittorneg Jan. 3, 1939. BRADEN 2,142,345

MAGNETRON APPARATUS Filed July 22, 1956 2 Sheets-Sheet 2 8g attorney Patented Jan. 3, 1939 UNITED STATES PATENT OFFICE MAGNETRON APPARATUS Delaware Application July 22, 1936, Serial No. 92,051

6 Claims.

This invention relates to magnetron apparatus and more particularly to a magnetron which employs a permanent magnet with an adjustable shunt for varying the magnetic field.

A magnetron is a device in which a cathode and cylindrical shape anode are concentrically mounted within an evacuated envelope. A magnetic field is applied so that its lines of force surround and are substantially parallel to the cathode. Under the influence of the magnetic field electrons emitted from the cathode follow curved paths toward the anode. If a suitable resonant circuit is connected betwen cathode and anode, oscillatory currents of ultra high frequency may be established in the resonant circuit. The frequency or wave length of the resonant circuit and the magnetic field must be properly related to establish the optimum oscillatory current. The ratio between the field and the Wave length is approximately such that the wave length in centimeters equals twelve thousand divided by the magnetic field in gauss.

An electromagnet may be readily used to establish the magnetic fields of desired density, but

an electromagnet, together with its power supply,

is not entirely suitable for portable equipment. While a permanent magnet may be substituted for the electromagnet, suitable provision should be made for varying the field strength at the pole of the permanent magnet. This invention contemplates a permanent magnet for a magnetron provided with suitable means for varying the density of the applied magnetic field.

One of the objects of this invention is to provide a permanent magnet structure for a magnetron.

Another object is to provide a permanent magnet with means for adjusting the density of the magnetic field at the pole pieces to thereby control a magnetron.

A further object is to provide a single control means for adjusting the density of the magnetic field and the frequency of the resonant circuit of a magnetron.

The invention may be best understood by reference to the accompanying drawings in which Figs. 1 and 2 represent, respectively, end and side elevational views of one embodiment of my invention,

Fig. 3 is a schematic diagram of a magnetron and a view, in perspective, of a permanent magnet with a variable shunt, and tunable output circuit which are adjusted by unicontrol means, and

Fig. 4 is a side elevational view of a permanent magnet with an adjustable shunt for controlling the magnetic field applied to a magnetron device.

Indescribing the several figures, the same reference numerals will be used to indicate similar parts. Referring to Figs. 1 and 2, on a suitable base I is pivotally mounted a non-ferrous U-shaped bracket 3. The bracket may be locked in position by the bolt 5 which projects through the base i. A pair of pole pieces 'l! of soft iron are secured to the ends of the U-shaped bracket. The pole pieces I, l are joined to one or more U-shaped permanent magnets 9.

A pair of face plates l I, ll of ferrous metal are clamped to either side of the pole pieces by bolts l3. pleted at the top by non-ferrous plates l5 which are secured to the face plates by bolts ll, rivets or the like. The upper ends of the non-ferrous plates are bent at right angles and form the bearings IQ for adjusting screws 2|. The adjusting screws 2| are maintained in the bearing l9 by suitable shoulders which take up the end thrust. Adjusting knobs 23 are secured to the screws 2|.

A pair of adjustable magnetic shunts 25 are engaged by the screws 2!. Suitable projections 21 at the ends of each shunt engage the sides of the face plates 9 and thereby form guides for the vertical adjustment of the shunts. The magnetic force is sufiicient to. securely hold the shunts to the surfaces of the face plates 9. It will be observed that the lower central part of each shunt is cut away to prevent the shunt from striking the magnetron tube 29 which is positioned be tween the pole pieces '1 and supported by a pair of brackets 3|.

The magnetron tube envelope may be flattened adjacent the pole pieces to thereby bring the pole pieces close to the anode and cathode elements. The details of the magnetron electrode arrangement have been omitted in Figs. 1 and 2 but may be seen in Fig. 3.

In the operation of the shunts in Figs. 1 and 2, the permanent magnets establish a strong field between the pole pieces when the shunts are at the uppermost position. When the shunts are moved to their lowermost position, a substantial portion of the magnetic lines of force formerly existing between the pole pieces are now transferred to the shunts and thus the magnetic density between the pole pieces is minimized. The actual adjustment is effected by rotating the adjusting screws 2| which are threaded into the shunts. It should be understood that a single shunt may be used, or two shunts may be used The face plates |IH are com- 1 with a suitable unicontrol or with separate controls.

In Fig. 3 a single permanent U-shaped magnet 33 is shown. A pair of pole pieces 35 are secured to the ends of the magnet. A magnetic shunt 31 is adjustably arranged on the surface of the magnet. The shunt may be equipped with guides, not shown, to prevent horizontal movement and permit vertical adjustment. The vertical adjustment is accomplished by an adjusting screw 3Q which is supported by a bearing in a bracket dd Collars 33 attached to the screw prevent motion along its axis. An adjusting knob 45 may be secured to the screw 39. A pulley 41, whose function will be described below, is also attached to the screw.

Within a magnetron envelope 49 are concentrically Supported a, cathode 5| and a pair of split cylindrical anodes 55. The cathode is connected to a battery 51, and the anodes are connected to the conductors of a transmission line The transmission line terminates in a dipole antenna H. An anode battery 63 is connected between the cathode battery and the central point of the dipole antenna. The positive terminal of the battery is connected to the dipole.

The transmission line 59 forms the resonant output circuit of the magnetron. The oscilla ory frequency of the transmission line may be adjusted by varying its effective length by means of a pair of trombones 55 or other suitable means. As pointed out above, the f eld density the optimum frequency of oscillation are related. Therefore, the length of the transmission line and the adjustment of the magnetic shunt may be related. This relation will not be linear and may vary for different magnets and different magnetrons.

The unicontrol for the shunt and the transmission line is effected by connecting the screw 35*; through a small pulley ll and belt Ei'l, or any type mechanical coupling of suitable radio, to a relatively larger pulley 69 which is fastened to a shaft ii. The shaft 1! is mounted on bearings 53 which are supported by any appropriate means. A disc '55 is secured to the shaft and a cam slot ll is cut in the disc. The actual shape of the cam slot may best be determined experimentally by noting the position of the trombones 55 for a series of adjustments of the magnetic shunts. A. cam follower i9 is located in the slot and secured to the trombones by an insulated link iii The link may be supported by guides, not shown.

The knob 55 turns the adjusting screw 39 which positions the shunt 31 and at the same time through the connecting belt 5? tunes the disc '55. By means of the cam slot Ti and connecting link 8! the effective length of the transmission line is adjusted to correspond with the optimum shunt position. Thus the unicontro1 between the magnetic shunt and resonant output circuit is made practical. 7

Instead of sliding the shunts as illustrated in Figs. 1, 2 and 3, the arrangement of Fig. 4. may

be employed. In Fig. 4 a plurality of U shaped permanent magnets 83 are clamped together by non-magnetic face plates 85. The upper ends of the face plates are bent to form a support for the member 8! which carry the magnetic shunts 81 The members 87 are connected by a biasing spring 94. The spring draws the shunt carrying members inwardly and causes them to engage the cam 53 which is rotatably supported within the permanent magnets. As the cam is rotated the shunts are displaced with respect to the pole pieces 95 which are positioned at the ends of the U shaped magnets. The maximum air gap between the shunt and pole pieces corresponds with maximum field intensity between the pole pieces. The minimum air gap between the shunts and pole pieces corresponds with minimum fiux density between the pole pieces. The arrangement of Fig. 4 may be used as indicated in Fig. 3 to effect unicontrol adjustment of the shunt and resonant circuit.

Thus I have described a magnetron device which may be used as an oscillator, detector or amplifier. The magnetic field is supplied by a permanent magnet which includes an adjustable magnetic shunt. Varying the position of the shunt varies the magnetic field applied to the magnetron. This variation in field changes the oscillation frequency, if the tube is operating as an oscillator, or changes the frequency to which it is sensitive if it is operating as a detector or amplifier.

When used as a detector or amplifier the incoming waves are impressedcn the antenna-and resulting output currents the anode circuit are impressed on a suitable signal responsive element. When used as an oscillator, the oscillatory currents are impressed on the antenna. Suitable means are provided for unicontrol of the tunable circuit and the magnetic s unt.

I claim as my invention:

1. A tunable magnetron oscillator which comprises a tube having cathode and anode electrodes and means including a variable magnetic field for producing oscillations in said tube which depend in frequency on the'strength' of said magnetic field, a variable tuning means connected between said electrodes, and unicontrol means for simultaneously varying the magnetic field and said tuning means to keep the frequency of the oscillations generated and the frequency of the tuned circuit substantially the same.

2. A tunable magnetron including in combination a tube having cathode and anode electrodes and means including an adjustable magnetic field for producing electronic oscillations in said tube. said oscillations having a frequency dependent upon the adjustment of said field, a variable tuning means connected between said electrodes, and a unicontrol means for simultaneously varying said tuning means and adjusting said field to keep the frequencies of said oscillations and said tuning means substantially the same.

3. A tunable magnetron including in combina tion a tube having cathode and anode electrodes and means including a magnetic field for producing electronic oscillations in said tube; means for varying the strength of said field and thereby varying the frequency of said oscillations; a tunable circuit connected between said electrodes; and a unicontrol means for varying said field varying means and varying said tunable circuit to keep the frequency of said oscillations and the frequency of said circuit substantially the same.

frequency of the oscillations generated and the frequency of the tuned circuit substantially the same.

5. In a magnetron oscillator, the combination of a magnetron including cathode and anode electrodes, a tunable circuit connected to said electrodes, means for tuning said circuit, means for establishing a magnetic field about said electrodes, means for varying the strength of said field whereby oscillations of a frequency dependent on said field strength are generated in said tube, and unicontrol means coupling said field varying means and said tuning means whereby each may be adjusted simultaneously to thereby efiect substantially optimum operation of said magnetron and said circuit at the same frequency.

6. In a magnetron oscillator, the combination of a magnetron including cathode and anode electrodes, a tunable circuit connected to said electrodes, means for tuning said circuit, a permanent magnet for establishing a magnetic field about said electrodes, a shunt for varying the strength of said field whereby oscillations of a frequency dependent on said field strength are generated in said tube, and unicontrol means coupling said shunt means and said tuning means whereby each may be adjusted simultaneously to thereby establish substantially optimum oscillations in said magnetron and in said circuit at the same frequency. 

